The ammonite faunas of the upper Hypselocyclum to Divisum zones (Lower Kimmeridgian, Upper Jurassic) at Małogoszcz, Holy Cross Mts., central Poland: their stratigraphical interpretation and evolutionary development

Abstract

The transgressive succession of deposits of the late Early Kimmeridgian at Małogoszcz in the south-western margin of the Holy Cross Mts. in central Poland yielded diversified faunas of ammonites. The commonly represented Submediterranean ataxioceratid ammonites include the last members of Ataxioceras in the Hypselocyclum Zone and the assemblage of various Crussoliceras, Garnierisphinctes and Progeronia, mostly developed in the Divisum Zone, and associated upwards (Uhlandi Subzone) with aspidoceratids (Pseudhimalayites). A few typical Mediterranean ammonites (Nebrodites, Presimoceras, Idoceras, Taramelliceras) are indicative of the Herbichi Zone. The Subboreal ammonites include mostly Eurasenia, Involuticeras in addition to some Rasenia and Rasenioides of the uppermost Cymodoce Zone, corresponding to the Askepta Subzone. The changes in composition of ammonite faunas and comparison with the coeval faunas of other areas of Europe give indications on the evolutionary development of some Ataxiocertidae and Aulacostephanidae at the end of Early Kimmeridgian. The development of the Crussoliceras, Garnierisphinctes and Progeronia, having possibly their roots in the Mediterranean areas, was strictly correlated with the overall transgression and oscillations of sea-level controlled possibly by climatic eccentricity cycles in northern Tethyan shelf. This resulted also in decline of older Ataxioceras and its nearby allies. The indigenous lineage of Aulacostephanidae includes the transition from Eurasenia to Pararasenia. The development from Rasenioides to Aulacostephanoides occurred mostly in the Subboreal areas – although some late representatives of Rasenioides like R. moeschi reached the area of study. The existence of an independent lineage leading from Rasenia involuta to heavily-ribbed Aulacostephanoides/Aulacostephanus is also suggested.